The present invention relates to a method of and apparatus for displaying digitally encoded video signals, and preferably for replaying such signals which have been recorded on a recording medium and at a speed different to that at which the signals have been recorded.
Although the bulk of the description is given in relation to the replaying of recorded information, the method and apparatus are equally useful for accepting transmitted digitally encoded video signals, say for instant replay in slow motion or for accepting one transmitted broadcast and synchronising that broadcast with another transmitter broadcast.
The most common existing recording medium is magnetic tape and at present there are two types of so called "helical scan" recording and playback apparatus for magnetic tape. The first type utilizes a revolving drum of relatively large diameter which in making one revolution records or plays back one complete field of a television picture from magnetic tape entrained on the surface of the drum. The information being recorded as an angled stripe on the tape. The second tape utilizes a drum of smaller diameter which revolves at a higher speed than the first type. In this case, one complete field is recorded on the tape in a number of segments, say 6, and for each revolution of the drum, one of the segments is played back. The first type will hereinafter be called a non-segmental apparatus and the second type, a segmental apparatus.
For non-segmented recorders there is an inevitable gap in information lasting several lines which is normally arranged to occur during field blanking.
Such a gap would also occur on segmented recorders, between segments, if only one head is used. To overcome this problem two heads are used, diametrically opposite one another, and the tape is wrapped about 190.degree. around the drum causing an overlap during which time switching from one head to the other occurs.
When editing video tape it is often only necessary to have a fairly good visual representation of the picture recorded on the tape and it is important that the tape can be run through faster than usual in order to save time. When using non-segmental type apparatus it is possible to run the tape through at a fairly rapid rate, say 5 or 6 times the normal rate and still produce a picture which is acceptable for editing purposes.
Further, if slow motion is required this cannot be achieved with a satisfactory picture quality without utilizing expensive ancilliary equipment.